Steroids as Agonists for FXR

ABSTRACT

The invention relates to compounds of formula (I): 
     
       
         
         
             
             
         
       
     
     wherein R is ethyl, propyl or allyl, and pharmaceutically acceptable salts, solvates or amino acid conjugates thereof. The compounds of formula (I) are useful as FXR agonists.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 13/761,889 (now allowed), filed Feb. 7, 2013, which is a continuation of U.S. patent application Ser. No. 13/288,558, filed Nov. 3, 2011, now U.S. Pat. No. 8,377,916, which is a continuation of U.S. patent application Ser. No. 12/547,147, filed Aug. 25, 2009, now U.S. Pat. No. 8,058,267, which is a continuation of U.S. patent application Ser. No. 11/602,307, filed Nov. 21, 2006, now U.S. Pat. No. 7,786,102, which is a continuation of U.S. patent application Ser. No. 10/471,549, filed Sep. 11, 2003, now U.S. Pat. No. 7,138,390, which claims priority under 35 U.S.C. Section 371 to PCT Patent Application No. PCT/EP02/01832, filed Feb. 21, 2002, which claims priority to U.S. Patent Application No. 60/274,959, filed Mar. 12, 2001, the disclosures of each of which are incorporated by reference herein in their entirety.

BACKGROUND OF THE INVENTION

The present invention relates to Farnesoid X receptors (FXR). More particularly, the present invention relates to compounds useful as agonists for FXR, pharmaceutical formulations comprising such compounds, and therapeutic use of the same.

Farnesoid X Receptor (FXR) is an orphan nuclear receptor initially identified from a rat liver cDNA library (B M. Forman, et al., Cell 81:687-693 (1995)) that is most closely related to the insect ecdysone receptor. FXR is a member of the nuclear receptor family of ligand-activated transcription factors that includes receptors for the steroid, retinoid, and thyroid hormones (D J. Mangelsdorf, et al., Cell 83:841-850 (1995)). Northern and in situ analysis show that FXR is most abundantly expressed in the liver, intestine, kidney, and adrenal (B M. Forman, et al., Cell 81:687-693 (1995) and W. Seol, et al., Mol. Endocrinnol. 9:72-85 (1995)). FXR binds to DNA as a heterodimer with the 9-cis retinoic acid receptor (RXR). The FXR/RXR heterodimer preferentially binds to response elements composed of two nuclear receptor half sites of the consensus AG(G/T)TCA organized as an inverted repeat and separated by a single nucleotide (IR-1 motif) (B M. Forman, et al., Cell 81:687-693 (1995)). An early report showed that rat FXR is activated by micromolar concentrations of farnesoids such as farnesol and juvenile hormone (B M. Forman, et al., Cell 81:687-693 (1995)). However, these compounds failed to activate the mouse and human FXR, leaving the nature of the endogenous FXR ligand in doubt. Several naturally-occurring bile acids bind to and activate FXR at physiological concentrations (PCT WO 00/37077, published 29 Jun. 2000)). As discussed therein, the bile acids that serve as FXR ligands include chenodeoxycholic acid (CDCA), deoxycholic acid (DCA), lithocholic acid (LCA), and the taurine and glycine conjugates of these bile acids.

Bile acids are cholesterol metabolites that are formed in the liver and secreted into the duodenum of the intestine, where they have important roles in the solubilization and absorption of dietary lipids and vitamins. Most bile acids (˜95%) are subsequently reabsorbed in the ileum and returned to the liver via the enterohepatic circulatory system. The conversion of cholesterol to bile acids in the liver is under feedback regulation: Bile acids down-regulate the transcription of cytochrome P450 7a (CYP7a), which encodes the enzyme that catalyzes the rate limiting step in bile acid biosynthesis. There are data to suggest that FXR is involved in the repression of CYP7a expression by bile acids, although the precise mechanism remains unclear (D W. Russell, Cell 97:539-542 (1999)). In the ileum, bile acids induce the expression of the intestinal bile acid binding protein (IBABP), a cytoplasmic protein which binds bile acids with high affinity and may be involved in their cellular uptake and trafficking Two groups have now demonstrated that bile acids mediate their effects on IBABP expression through activation of FXR, which binds to an IR-1 type response element that is conserved in the human, rat, and mouse IBABP gene promoters (14;17). Thus FXR is involved in both the stimulation (IBABP) and the repression (CYP7a) of target genes involved in bile acid and cholesterol homeostasis.

European Patent No. 0 312 867, published 05 May 1992 to Giuliana S.p.A. describes 6-methyl derivatives of natural biliary acids such as ursodeoxycholic acid, ursocholic acid, chenodeoxycholic acid and cholic acid.

BRIEF SUMMARY OF THE INVENTION

According to a first aspect, the present invention provides compounds of formula I:

wherein R is ethyl, and pharmaceutically acceptable salts, solvates or amino acid conjugates thereof. In one preferred embodiment, the compound of formula (I) is in the form of the glycine or taurine conjugate. In another aspect, the present invention provides 3α,7α-dihydroxy-6α-ethyl-5β-cholan-24-oic acid and pharmaceutically acceptable salts, solvates or amino acid conjugates thereof.

In another aspect, the present invention provides compounds which are FXR agonists.

In another aspect, the present invention provides a pharmaceutical formulation comprising a compound of formula (I) and a pharmaceutically acceptable carrier or diluent.

In another aspect, the present invention provides a method for the prevention or treatment of an FXR mediated disease or condition. The method comprises administering a therapeutically effective amount of a compound of formula (I). The present invention also provides the use of a compound of formula (I) for the preparation of a medicament for the prevention or treatment of an FXR mediated disease or condition.

In another aspect, the present invention provides a method for the prevention or treatment of cardiovascular disease. The method comprises administering a therapeutically effective amount of a compound of formula (I). The present invention also provides the use of a compound according to claim 1 for the preparation of a medicament for the prevention or treatment of cardiovascular disease. In one embodiment, the cardiovascular disease is atherosclerosis.

In another aspect, the present invention provides a method for increasing HDL cholesterol. The method comprises administering a therapeutically effective amount of a compound of formula (I). The present invention also provides the use of a compound according to claim I for the preparation of a medicament for increasing HDL-cholesterol.

In another aspect, the present invention provides a method for lowering triglycerides. The method comprises administering a therapeutically effective amount of a compound of formula (I). The present invention also provides the use of a compound according to claim 1 for the preparation of a medicament for lowering triglycerides.

In another aspect, the present invention provides a method for the prevention or treatment of cholestatic liver disease. The method comprises administering a therapeutically effective amount of a compound of formula (I). The present invention also provides the use of a compound according to claim 1 for the preparation of a medicament for the prevention or treatment of cholestatic liver diseases.

In another aspect, the present invention provides a radiolabeled compound of formula (I). In one embodiment, the compound of formula (I) is tritiated.

In another aspect, the present invention provides a process for preparing a compound of formula (I) and pharmaceutically acceptable salts, solvates or amino acid conjugates thereof. The process comprises the steps of:

a) reacting 3α-hydroxy-7-keto-5β-cholan-24-oic acid with 3,4-dihydropyrane to prepare 3α-tetrahydropyranyloxy-7-keto-5β-cholan-24-oic acid;

b) reacting 3α-tetrahydropyranyloxy-7-keto-5β-cholan-24-oic acid with an alkyl bromide of the formula R-Br where R is ethyl to prepare a compound of formula (II)

wherein R is ethyl;

c) reacting the compound of formula (II) with sodium borohydride to prepare a compound of formula (III)

and

d) reacting the compound of formula (III) with sodium hydroxide to prepare the compound of formula (I).

Further aspects of the present invention are described in the detailed description of the invention, examples, and claims which follow.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides compounds of formula I:

wherein R is ethyl and pharmaceutically acceptable salts, solvates or amino acid conjugates thereof.

Suitable pharmaceutically acceptable salts according to the present invention will be readily determined by one skilled in the art and will include, for example, basic salts such as metallic salts made from aluminium, calcium, lithium, magnesium, potassium, sodium, and zinc or organic salts made from N, N¹-dibenzylethylenediamine, chlorprocaine, choline, diethanolamine, ethylendiamine, meglumine (N-methylglucamine), and procaine. Such salts of the compounds of formula (I) may be prepared using conventional techniques, from the compound of Formula (I) by reacting, for example, the appropriate base with the compound of Formula (I).

When used in medicine, the salts of a compound of formula (I) should be pharmaceutically acceptable, but pharmaceutically unacceptable salts may conveniently be used to prepare the corresponding free base or pharmaceutically acceptable salts thereof

As used herein, the term “solvate” is a crystal form containing the compound of formula (I) or a pharmaceutically acceptable salt thereof and either a stoichiometric or a non-stoichiometric amount of a solvent. Solvents, by way of example, include water, methanol, ethanol, or acetic acid. Hereinafter, reference to a compound of formula (I) is to any physical form of that compound, unless a particular form, salt or solvate thereof is specified.

As used herein, the term “amino acid conjugates” refers to conjugates of the compounds of formula (I) with any suitable amino acid. Preferably, such suitable amino acid conjugates of the compounds of formula (I) will have the added advantage of enhanced integrity in bile or intestinal fluids. Suitable amino acids include but are not limited to glycine and taurine. Thus, the present invention encompasses the glycine and taurine conjugates of any of the compounds of formula (I).

Preferred compounds of formula (I) include 3α,7α-dihydroxy-6α-ethyl-5β-cholan-24-oic acid and its pharmaceutically acceptable salts, solvates or amino acid conjugates thereof

Hereinafter all references to “compounds of formula (I)” refer to compounds of formula (I) as described above together with their and pharmaceutically acceptable salts, solvates or amino acid conjugates thereof.

Preferably, the compounds of formula (I) are FXR agonists. As used herein, the term “agonist” refers to compounds which achieve at least 50% activation of FXR relative to CDCA, the appropriate positive control in the assay methods described in PCT Publication No. WO 00/37077 published 29 Jun. 2000 to Glaxo Group Limited, the subject matter of which is incorporated herein by reference in its entirety. More preferably, the compounds of this invention achieve 100% activation of FXR in the scintillation proximity assay or the HTRF assay as described in PCT Publication No. WO 00/37077.

The compounds of the formula (I) are useful for a variety of medicinal purposes. The compounds of formula (I) may be used in methods for the prevention or treatment of FXR mediated diseases and conditions. FXR mediated diseases or conditions include cardiovascular diseases including atherosclerosis, arteriosclerosis, hypercholesteremia, and hyperlipidemia. In particular, the compounds of formula (I) are useful in the treatment and prevention of cardiovascular disease including atherosclerosis and hypercholesteremia. The compounds of formula (I) are also useful for increasing HDL-cholesterol, and lowering triglycerides.

In addition, the compounds of the present invention are useful for the prevention and treatment of cholestatic liver diseases. The compounds of the present invention increase the flow of bile acid. Increased flow of bile acids improves the flux of bile acids from the liver to the intestine. See, C. Sinal, Cell 102: 731-744 (2000). Essentially, FXR null mice demonstrate that FXR plays a central role in bile acid homeostasis, and is therefore critical to lipid homeostasis by virtue of the regulation of enzymes and transporters that are critical to lipid catabolism and excretion. FXR therefore is an important target for the treatment of a number of cholestatic liver diseases and other lipid related diseases and conditions.

The methods of the present invention are useful for the treatment of mammals generally and particularly humans.

The methods of the present invention comprise the step of administering a therapeutically effective amount of the compound of formula (I). As used herein, the term “therapeutically effective amount” refers to an amount of the compound of formula (I) which is sufficient to achieve the stated effect. Accordingly, a therapeutically effective amount of a compound of formula (I) used in the method for the prevention or treatment of FXR mediated diseases or conditions will be an amount sufficient to prevent or treat the FXR mediated disease or condition. Similarly, a therapeutically effective amount of a compound of formula (I) for use in the method for the prophylaxis or treatment of cholestatic liver diseases or increasing bile flow will be an amount sufficient to increase bile flow to the intestine.

The amount of a compound of formula (I) or pharmaceutically acceptable salt or solvate thereof, which is required to achieve the desired biological effect will depend on a number of factors such as the use for which it is intended, the means of administration, and the recipient, and will be ultimately at the discretion of the attendant physician or veterinarian. In general, a typical daily dose for the treatment of FXR mediated diseases and conditions, for instance, may be expected to lie in the range of from about 0.01 mg/kg to about 100 mg/kg. This dose may be administered as a single unit dose or as several separate unit doses or as a continuous infusion. Similar dosages would be applicable for the treatment of other diseases, conditions and therapies including the prophylaxis and treatment of cholestatic liver diseases.

Thus in a further aspect the present invention provides pharmaceutical compositions comprising, as active ingredient, a compound of formula (I) or a pharmaceutically acceptable salt or solvate thereof, together with at least one pharmaceutical carrier or diluent. These pharmaceutical compositions may be used in the prophylaxis and treatment of the foregoing diseases or conditions and in cardiovascular therapies as mentioned above.

The carrier must be pharmaceutically acceptable and must be compatible with, i.e. not have a deleterious effect upon, the other ingredients in the composition. The carrier may be a solid or liquid and is preferably formulated as a unit dose formulation, for example, a tablet which may contain from 0.05 to 95% by weight of the active ingredient. If desired other physiologically active ingredients may also be incorporated in the pharmaceutical compositions of the invention.

Possible formulations include those suitable for oral, sublingual, buccal, parenteral (for example subcutaneous, intramuscular, or intravenous), rectal, topical including transdermal, intranasal and inhalation administration. Most suitable means of administration for a particular patient will depend on the nature and severity of the disease or condition being treated or the nature of the therapy being used and on the nature of the active compound, but where possible, oral administration is preferred for the prevention and treatment of FXR mediated diseases and conditions.

Formulations suitable for oral administration may be provided as discrete units, such as tablets, capsules, cachets, lozenges, each containing a predetermined amount of the active compound; as powders or granules; as solutions or suspensions in aqueous or non-aqueous liquids; or as oil-in-water or water-in-oil emulsions.

Formulations suitable for sublingual or buccal administration include lozenges comprising the active compound and, typically a flavoured base, such as sugar and acacia or tragacanth and pastilles comprising the active compound in an inert base, such as gelatine and glycerine or sucrose acacia.

Formulations suitable for parenteral administration typically comprise sterile aqueous solutions containing a predetermined concentration of the active compound; the solution is preferably isotonic with the blood of the intended recipient. Additional formulations suitable for parenteral administration include formulations containing physiologically suitable co-solvents and/or complexing agents such as surfactants and cyclodextrins. Oil-in-water emulsions are also suitable formulations for parenteral formulations. Although such solutions are preferably administered intravenously, they may also be administered by subcutaneous or intramuscular injection.

Formulations suitable for rectal administration are preferably provided as unit-dose suppositories comprising the active ingredient in one or more solid carriers forming the suppository base, for example, cocoa butter.

Formulations suitable for topical or intranasal application include ointments, creams, lotions, pastes, gels, sprays, aerosols and oils. Suitable carriers for such formulations include petroleum jelly, lanolin, polyethyleneglycols, alcohols, and combinations thereof.

Formulations of the invention may be prepared by any suitable method, typically by uniformly and intimately admixing the active compound with liquids or finely divided solid carriers or both, in the required proportions and then, if necessary, shaping the resulting mixture into the desired shape.

For example a tablet may be prepared by compressing an intimate mixture comprising a powder or granules of the active ingredient and one or more optional ingredients, such as a binder, lubricant, inert diluent, or surface active dispersing agent, or by moulding an intimate mixture of powdered active ingredient and inert liquid diluent.

Suitable formulations for administration by inhalation include fine particle dusts or mists which may be generated by means of various types of metered dose pressurised aerosols, nebulisers, or insufflators.

For pulmonary administration via the mouth, the particle size of the powder or droplets is typically in the range 0.5-10 μm, preferably 1-5 μm, to ensure delivery into the bronchial tree. For nasal administration, a particle size in the range 10-500 μm is preferred to ensure retention in the nasal cavity.

Metered dose inhalers are pressurised aerosol dispensers, typically containing a suspension or solution formulation of the active ingredient in a liquefied propellant. During use, these devices discharge the formulation through a valve adapted to deliver a metered volume, typically from 10 to 150 μl, to produce a fine particle spray containing the active ingredient. Suitable propellants include certain chlorofluorocarbon compounds, for example, dichlorodifluoromethane, trichlorofluoromethane, dichlorotetrafluoroethane and mixtures thereof. The formulation may additionally contain one or more co-solvents, for example, ethanol surfactants, such as oleic acid or sorbitan trioleate, anti-oxidants and suitable flavouring agents.

Nebulisers are commercially available devices that transform solutions or suspensions of the active ingredient into a therapeutic aerosol mist either by means of acceleration of a compressed gas typically air or oxygen, through a narrow venturi orifice, or by means of ultrasonic agitation. Suitable formulations for use in nebulisers consist of the active ingredient in a liquid carrier and comprising up to 40% w/w of the formulation, preferably less than 20% w/w. The carrier is typically water or a dilute aqueous alcoholic solution, preferably made isotonic with body fluids by the addition of, for example, sodium chloride. Optional additives include preservatives if the formulation is not prepared sterile, for example, methyl hydroxy-benzoate, anti-oxidants, flavouring agents, volatile oils, buffering agents and surfactants.

Suitable formulations for administration by insufflation include finely comminuted powders which may be delivered by means of an insufflator or taken into the nasal cavity in the manner of a snuff. In the insufflator, the powder is contained in capsules or cartridges, typically made of gelatin or plastic, which are either pierced or opened in situ and the powder delivered by air drawn through the device upon inhalation or by means of a manually-operated pump. The powder employed in the insufflator consists either solely of the active ingredient or of a powder blend comprising the active ingredient, a suitable powder diluent, such as lactose, and an optional surfactant. The active ingredient typically comprises from 0.1 to 100 w/w of the formulation.

In addition to the ingredients specifically mentioned above, the formulations of the present invention may include other agents known to those skilled in the art of pharmacy, having regard for the type of formulation in issue. For example, formulations suitable for oral administration may include flavouring agents and formulations suitable for intranasal administration may include perfumes.

Therefore, according to a further aspect of the present invention, there is provided the use of a compound of formula (I) in the preparation of a medicament for the prevention or treatment of FXR mediated diseases or conditions.

Compounds of the invention can be made according to any suitable method of organic chemistry. According to one method, compounds of formula (I) are prepared using the synthesis process as depicted in Scheme 1:

wherein R is ethyl.

Generally, the compounds of the present invention can be prepared by the process comprising a) reacting 3α-hydroxy-7-keto-5β-cholan-24-oic acid with 3,4-dihydropyrane to prepare 3α-tetrahydropyranyloxy-7-keto-5β-cholan-24-oic acid; b) reacting 3α-tetrahydropyranyloxy-7-keto-5β-cholan-24-oic acid with an alkyl bromide of the formula R-Br where R is ethyl to prepare a compound of formula (II); c) reacting the compound of formula (II) with sodium borohydride to prepare a compound of formula (III); d) reacting the compound of formula (III) with sodium hydroxide to prepare the compound of formula (I).

More particularly, the compounds of formula (I) are conveniently prepared by reacting the compounds of formula (III) with sodium hydroxide in a suitable solvent at ambient temperature. Suitable solvents include lower alcohols, such as ethanol. The reaction mixture may optionally be acidified with an appropriate acid such as hydrochloric acid.

The compounds of formula (III) are conveniently prepared by reacting compounds of formula (II) with sodium borohydride in a suitable solvent at ambient temperature. Suitable solvents include lower alcohols such as ethanol.

The compounds of formula (II) are conveniently prepared by reacting 3α-tetrahydropyranyloxy-7-keto-5β-cholan-24-oic acid with an alkyl bromide of the formula R-Br where R is ethyl in a suitable solvent and in the presence of n-Butyl lithium and HMPA in diisopropylamine. Polar solvents such as tetrahydrofuran are useful for conducting the reaction. Preferably, the reaction is carried out at cold temperatures such as about −70 to −80° C.

3α-Tetrahydropyranyloxy-7-keto-5β-cholan-24-oi acid can conveniently be prepared from 3α-hydroxy-7-keto-5β-cholan-24-oic acid by reacting with 3,4-dihydropyrane in p-toluenesulfonic acid.

Pharmaceutically acceptable salts, solvates and amino acid conjugates of the compounds of formula (I) can be prepared from the free base using methods known to those skilled in the art.

The present invention also provides radiolabeled compounds of formula (I). Radiolabeled compounds of formula (I) can be prepared using conventional techniques. For example, radiolabeled compounds of formula (I) can be prepared by reacting the compound of formula (I) with tritium gas in the presence of an appropriate catalyst to produce radiolabeled compounds of formula (I). In one preferred embodiment, the compounds of formula (I) are tritiated.

The radiolabeled compounds of formula (I) are useful in assays for the identification of compounds which interact with FXR such as those described in PCT Publication No. WO 00/37077 already incorporated herein.

The following examples are intended for illustration only and are not intended to limit the scope of the invention in any way, the present invention being defined by the claims.

Example: Synthesis of 3α7α-Dihydroxv-6α-ethyl-5β-cholan-24-oic Acid (6aEt-CDCA)

3α-Tetrahydropyranyloxy-7-keto-5β-cholan-24-oic acid.

p-Toluensulfonic acid (6.0 g, 3.2 mmol) and 3,4-dihydro-2H-pyrane (4.6 g, 54 mmol) were added to a solution of 3α-hydroxy-7-keto-5β-cholan-24-oic acid (1) (6.0 g, 14.4 mmol) in 120 ml of dioxane. The reaction mixture was stirred at room temperature for 15 min and then was treated with methanol saturated with ammonia until it reached pH of about 8-9. The solvents were removed under vacuum and the residue was extracted with chloroform (200 ml) and washed with a saturated NaHCO₃ solution (2×50 ml). After drying over anhydrous Na₂SO₄ and evaporation under vacuum, the residue was purified by silica gel chromatography. Elution by CHCl₃:MeOH (90:10) yielded 5.4 g (10.4 mmol, 74% yield) of compound 2 as a white solid (mp: 157-159° C.).

¹H-NMR (CDCl₃) δ: 0.58 (s, 3H, CH₃-18); 0.88 (d, J=6.1 Hz, 3H, CH₃-21); 1.14 (s, 3H, CH₃-19); 3.3-3.7 (m, 3H, pyr); 3.75-3.95 (m, 1H, pyr); 4.64-4.71 (m, 1H, CH-3).

Ethyl 3α-hydroxy-6α-ethyl-7-keto-5β-cholan-24-oate.

n-Butyl lithium (21.1 ml, 1.6M solution in hexane) and HMPA (4.3 ml) were added dropwise at −78° C. to a solution of diisopropylamine (4.1 ml, 33.7 mmol) in 250 ml of dry THF. The system was held at −78° C. for an additional 30 min and then, 3α-tetrahydropyranyloxy-7-keto-5β-cholan-24- oic acid (2) (5 g, 10.5 mmol) dissolved in 50 ml of dry THF was cooled to −78° C. and added dropwise to the mixture. After 20 minutes ethyl bromide (7.8 ml, 105 mmol) dissolved in THF (20 ml) was slowly added and the mixture was allowed to come to room temperature overnight. The solvents were removed under vacuum, acidified by 10% HCl and extracted with ethyl acetate (5×200 ml), and washed with a saturated NaCl solution (1×200 ml). After drying over anhydrous Na₂SO₄ and evaporation under vacuum, the crude residue was refluxed with a solution of 2N HCl in EtOH (50 ml) for 12 hours. The residue was evaporated under vacuum and extracted with ethyl acetate (300 ml), washed with a saturated NaHCO₃ solution (2×100 ml), dried with Na₂SO₄ and evaporated under vacuum. The residue was purified by silica gel chromatography; elution by light petroleum:ethyl acetate (70:30) yielded 0.57 g (1.27 mmol, 12% yield) of ethyl 3α-hydroxy-6α-ethyl-7-keto-5β-cholan-24-oate (3) as an amorphous solid.

¹H-NMR (CDCl₃) δ: 0.50 (s, 3H, CH₃-18); 0.69 (t, J=7.3 Hz, 31-1, CH₂—CH); 0.82 (d, J=6.2 Hz, 3H, CH₃-21); 1.06-1.18 (m, 8H, CO₂ CH₂CH₃+CH₂—CH₃+CH₃−19); 3.36-3.42 (m, 1H, CH—OH), 4.01 (q, J=7.2, Hz 2H, CO₂ CH₇CH₃).

Ethyl 3α,7α-dihydroxy-6α-ethyl-5β-cholan-24-oate.

Ethyl 3α-hydroxy-6α-ethyl-7-keto-5β-cholan-24-oate (3) (0.185 g, 0.4 mmol) was dissolved in 30 ml of 96% EtOH and treated with NaBH₄ (30 mg, 0.8 mmol). The mixture was stirred at room temperature for 2 hours. Water (10 ml) was then added and the mixture was partially concentrated under vacuum and extracted with ethyl acetate (3×20 ml). The combined organic fractions were washed with a saturated NaCl solution (1×50 ml), dried with Na₂SO₄ and evaporated under vacuum. To give ethyl 3α,7α-dihydroxy-6α-ethyl-5β-cholan-24-oate (4) (0.15 g, 0.33 mmol, 81% yield) as white solid (mp: 55-57° C.).

¹H-NMR (CDCl₃) δ: 0.62 (s, 3H, CH₃-18); 0.84-0.92 (m, 9H, CH₂—CH₃+CH₃-19+CH₃-21); 1.22 (t, J=7.2 Hz, 3H, CO₂ CH₂CH3); 3.30-3.47 (m, 1H, CH-3), 3.66 (brs, 1H, CH-7); 4.08 (q, J=7.2, Hz 2H, CO₂ CH₂CH₃).

3α, 7α-Dihydroxy-6α-ethyl-5β-cholan-24-oic acid. Ethyl 3α,7α-dihydroxy-6α-ethyl-5β-cholan-24-oate (4) (0.10 g, 0.22 mmol) was dissolved in 15 ml of 96% EtOH and added to 10% NaOH in 96% EtOH (2 ml, 5 mmol). The mixture was refluxed for 4 hours. The mixture was acidified with 3N HCl and extracted with ethyl acetate (3×20 ml). The combined organic fractions were washed with a saturated NaCl solution (1×50 ml), dried with Na₂SO₄ and evaporated under vacuum. The residue was chromatographed on silica gel column; elution by CHCl₃:MeOH (95:5) yielded 3α,7α-dihydroxy-6α-methyl-5β-cholan-24-oic acid (6) (0.04 g, 0.095 mmol, 43% yield).

¹H-NMR (CDCl₃) δ: 0.67 (s, 3H, CH₃-18); 0.90-0.96 (m, 9H, CH₂—CH₃+CH₃-19+CH₃-21); 2.22-2.46 (2m, 2H, CH₂-23); 3.39-3.47 (m, 1H, CH-3), 3.72 (brs, 1H, CH-7).

¹³C-NMR (CDCl₃) δ: 11.65, CH₂CH₃-6; 11.80, C-18; 18.25, C-21, 20.76, C-11; 22.23, CH₂CH₃-6; 23.14, C-19; 23.69, C-15; 28.17, C-16; 30.53, C-2; 30.81, C-22; 30.95, C-23; 33.23, C-9; 33.90, C-10; 35.38, C-20; 35.52, C-1; 35.70, C-4; 39.60, C-12; 40.03, C-5; 41.19, C-6; 42.77, C-13; 45.19, C-8; 50.49, C-14; 55.80, C-17; 70.97, C-7; 72.38, C-3; 179.19, C-24. 

What is claimed:
 1. A compound of formula I:

wherein R is ethyl or a pharmaceutically acceptable salt, solvate or amino acid conjugate thereof. 